Low Temperature Preparation Of Two Kinds Of Magnetic Photocatalyst With Shell/Shell/Core Structure And Its Photocatalytic Activity And Magnetic Recovery

Semiconductor photocatalysts,mainly titania,is considered to be one of the most promising green material for treating organic pollutants in water,because of its high oxidative power,high catalytic activity,chemical stability,mild reaction conditions,nontoxic,low cost and without secondary pollution.In water and wastewater treatment field,a slurry type reactor is the most commonly applied method because of its high specific surface area and dispersion.However,the use of TiO2slurry reactor is still limited mainly due to difficult separation of TiO2particles from treated water.If direct emissions not only cause secondary pollution,but also resulting the processing costs rise rapidly.To overcome the problem,TiO2loads on glass,ceramics and other lump materials have been prepared.But,the efficiency of TiO2photocatalyst is decreases considerably.In order to achieve high catalytic efficiency and recovery for repeating use,studies usually use superparamagnetic materials for the magnetic core,then directly coats TiO2on the magnetic core,or coats inorganic materials such as SiO2as an inert barrier on the magnetic core,followed by coats TiO2on the magnetic core which had be modified by inorganic materials.However, there are many disadvantage in the preparation process of these magnetic photocatalyst,such as the degradation of magnetic recovery performance for composite magnetic materials and calcine in high temperature,all these restrict the application of TiO2industrialized.To solve the above problems,this study synthesis nano-titanium dioxide phtocatalyst,and it was prepared by hydrolysis in the condition of low temperature(90℃) and the neutral environment(pH is about7).Then,fabrication two kinds of shell/shell/nuclear magnetically responsive titania catalyst,named TiO2/Al2O3/Fe3O4and TiO2/PS/FesO4，which consist of a magnetic core surrounded by titania shell.The magnetic core (Fe3O4nanoparticles) was modified respectively with aluminum oxide and polystyrene as inert isolating layer.The phase composition, morphology,surface properties and magnetic properties of the composite particles were characterized by X-ray diffraction(XRD), transmission electron microscopy (TEM), fourier infrared photometer (FT-IR) and vibrating sample magnetometer (VSM).The photocatalytic activity is determined respectively by the reaction rate constant K values for degradation of phenol and deoxygenize Cr(Ⅵ), which initial concentration are both 25mg-L"1.The magnetic recovery rate of magnetic photocatalyst is investigated by self-made magnetic recovery equipment,and the life of magnetic photocatalyst is inspected by repeated experiments.Through research,this paper obtained the following conclusions:1.Nano-titanium dioxide phtocatalyst was prepared by hydrolysis in the condition of low temperature.Design orthogonal experiment,and choose three factors:molar ratio of water and titanium, molar ratio of alcohol and titanium,and reaction reflus time.Then study three factors impact on the phtocatalytic activity of TiO2at three three levels.The optimal route of preparation TiO2as follows:Ethanol used as solvent,the molar ratio of water,ethanol and titanium is50:30:1,the reaction reflus time is6hours at90℃.2. The magnetic photocatalyst named TiO2/Al2O3/Fe3O4is consisted of a magnetic core surrounded by titania shell.The magnetic core (Fe3O4nanoparticles) was modified with Al2O3as inert isolating layer.Synthesized different magnetic photocatalysts in different conditions such as:different molar ratio of titanium and Fe3O4, different molar ratio of Al2O3and Fe3O4.Evalute the photocatalytic activity of magnetic photocatalysts which we had prepared.Finally,choose the best magnetic photocatalyst.The result shows that the magnetic named TAF6(molar ratio of the magnetic photocatalyst is nTiO2:n Al2O3nFe3O4=60:5:1) has a high photocatalytic activity. The photocatalytic degradation of phenol followed first order reaction and the reaction rate constant K of the TAF6was0.0223,after recycled5times, the K reduced only0.0041. The photocatalytic deoxygenize Cr(VI) also followed first order reaction and the reaction rate constant K of the TAF6was0.0123. The magnetic catalyst TAF6has a strong magnetic induction and a well magnetic recovery,In the experiment of degradation of phenol and deoxygenize Cr(VI), after recycled5times, the average recovery rate reached85.06%and80.05%respectively.3. The magnetic photocatalyst named TiO2/PS/Fe3O4is consisted of a magnetic core surrounded by titania shell.The magnetic core (Fe3O4nanoparticles) was modified with polystyrene as inert isolating layer.Synthesized different magnetic photocatalysts in different conditions such as:different molar ratio of titanium and Fe3O4, different molar ratio of Al2O3and Fe3O4.Evalute the photocatalytic activity of magnetic photocatalysts which we had prepared.Finally,choose the best magnetic photocatalyst.The result shows that the magnetic named TPF6(molar ratio of the magnetic photocatalyst is nTiO2:nSt:nFe3O4=60:2.5:1) has a high photocatalytic activity.The photocatalytic degradation of phenol followed first order reaction and the reaction rate constant K of the TPF6was0.0265.After recycled5times,the K reduced only0.0038.The photocatalytic deoxygenize Cr(Ⅵ) also followed first order reaction and the reaction rate constant K of the TPF6was0.0232.The magnetic catalyst TPF6has a strong magnetic induction and a well magnetic recovery.In the experiment of degradation of phenol and deoxygenize Cr(Ⅵ),after recycled5times,the average recovery rate reached92.7%and88.36%respectively.The magnetic photocatalyst which use polystyrene as inert isolating layer,can overcome the adverse effects such as:photocatalytic activity and magnetic recovery are both in decline.The magnetic photocatalyst TPF6can satisfy actual production needs, and compared with P25,it can be widely used in the process of industrialization.4. Compare TAF6and TPF6from the aspect of photocatalytic activity,magnetic recycling performance and the life of magnetic photocatalyst.The results show that,the catalytic activity of TPF6is higher than that of TAF6,the magnetic induction intensity of TPF6is stronger than that of TAF6,and the life of magnetic photocatalyst of TPF6is better than that of TAF6.The organic macromolecule polymers are more excellent than the inorganic materials as inert isolating layer,coated on magnetic core is also tighter and more uniform.The organic macromolecule polymers as inert isolating layer,not only maintain high photocatalytic activity of magnetic TiO2,but also have good magnetic recycling performance.